linux-kernel - Re: [RFC][PATCH 3/3] math128, x86_64: Implement {mult,add}

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Message-ID: <1335287973.28150.213.camel@twins>
Date:	Tue, 24 Apr 2012 19:19:33 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juri Lelli <juri.lelli@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 3/3] math128, x86_64: Implement {mult,add}_u128 in
 64bit asm

On Tue, 2012-04-24 at 10:17 -0700, H. Peter Anvin wrote:
> On 04/24/2012 09:36 AM, Peter Zijlstra wrote:
> > On Tue, 2012-04-24 at 09:34 -0700, H. Peter Anvin wrote:
> >> On 04/24/2012 09:10 AM, Peter Zijlstra wrote:
> >>
> >> Are you sure that gcc won't simply generate this code already if given
> >> "unsigned __int128"?
> > 
> > It might, but I've been told some GCC versions had issues, also lots of
> > archs fall back to libgcc functions.
> > 
> 
> Yes, but this is specific to x86-64.  If gcc can generate the code it
> can also schedule the code, which it can't for assembly...

Ok, but are you sure unsigned __int128 works for all gcc versions we
support?
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